Then 2s=2×( 1/2+ 1/2? + 1/2? +...............n) 1+ 1/2+ 1/2? + 1/2? + 1/2 (N- 1)
2s-s = 1+ 1/2+ 1/2? + 1/2? (n- 1)-( 1/2+ 1/2? + 1/2? +.............. 1/2 n)
So s =1-1/2 n.